1. Field of the Invention
This invention relates to a process for preparing certain ortho-substituted benzoic acids and to novel benzoic acids produced from this process.
2. Discussion of Background
The subject compounds are intermediates in the production of pesticides, for example as described in European Patent No. 0418175. Many literature methods are described for the preparation of orth-substituted benzoic acids. Where an ortho-substituent is introduced to the benzene ring via lithiation of the ortho-position of the ring, for example using the methods reviewed by Snieckus et al, Chem. Rev. (1990) Vol. 9 (6) pp 880-931, the reaction invariably involves protecting the carboxylic acid group. Gschwend and Rodriguez, Organic Reactions, Volume 26, Chapter 1 p 68 state that the direct ortho lithiation of arylcarboxylic acids is generally not feasible because of the increased electrophilicity of the carboxylate group. Where direct lithiation of aryl carboxylic acids is reported the reaction has been performed on non-phenyl ring systems, for example as described by S. Yu and B. Keay, J. Chem. Soc. (Perk. Trans. I) 1991, page 2600 to 2601 where 2-(t-butyldimethylsilyl)-3-furoic acid was lithiated in the four-position. In a number of literature references this problem is overcome by protecting the carboxylic acid group of the benzoic acid prior to lithiating the phenyl ring. For example Meyers et al, Tetrahedron Letters, (1983), Vol. 45 pp 4935-49 describe the use of an oxazoline protecting group to lithiate in the ortho position of a benzoic acid.
The present invention seeks to provide a method for introducing an ortho-substituent to a benzoic acid derivative via a lithiation in the ortho position without the need to protect the carboxylic acid group. This offers advantages by reducing the number of reaction steps needed to produce a required compound (since there is no need to introduce and subsequently remove a protecting group) for example by reducing the cost of synthesizing a compound (since there may be less synthetic steps in the reaction sequence) and by reducing the volume of waste chemicals that need to be disposed of in a reaction sequence.